Biosensor Device and Related Method

ABSTRACT

A device includes a biosensor, a sensing circuit electrically connected to the biosensor, a quantizer electrically connected to the sensing circuit, a digital filter electrically connected to the quantizer, a selective window electrically connected to the digital filter, and a decision unit electrically connected to the selective window.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a divisional of and claims priority to U.S.application Ser. No. 14/075,813, filed on Nov. 8, 2013 and issued asU.S. Pat. No. 9,702,846 on Jul. 11, 2017, entitled “Biosensor Device andRelated Method,” which application is hereby incorporated herein byreference in its entirety.

BACKGROUND

The semiconductor industry has experienced rapid growth due toimprovements in the integration density of a variety of electroniccomponents (e.g., transistors, diodes, resistors, capacitors, etc.). Forthe most part, this improvement in integration density has come fromshrinking the semiconductor process node (e.g., shrinking the processnode towards the sub-20 nm node). Another semiconductor industryexperiencing rapid growth is the microelectromechanical systems (MEMS)industry. MEMS devices are found in a variety of applications, rangingfrom automotive electronics to smartphones, and even biomedical devices.

Biomedical MEMS (BioMEMS) devices perform a variety of functions. A pHsensor is one type of BioMEMS device that electronically determines pHof a solution in contact with the pH sensor. The pH sensor may be usedin disease detection, organ tissue monitoring, water contaminationidentification, or myriad other practical applications.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram showing a biosensor system in accordance withvarious embodiments of the present disclosure;

FIG. 2 is a flowchart of a method in accordance with various embodimentsof the present disclosure;

FIG. 3 is a circuit block diagram showing a biosensor system withinternal calibration in accordance with various embodiments of thepresent disclosure;

FIGS. 4, 5, and 6 are diagrams showing a calibration path, and a deviceunder test (DUT) of the calibration path in accordance with variousembodiments of the present disclosure; and

FIG. 7 is a flowchart of a method for calibrating a biosensor system inaccordance with various embodiments of the present disclosure.

DETAILED DESCRIPTION

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the disclosedsubject matter, and do not limit the scope of the different embodiments.

Embodiments will be described with respect to a specific context, namelybiosensor circuits and related methods. Other embodiments may also beapplied, however, to other types of sensing circuits.

Throughout the various figures and discussion, like reference numbersrefer to like objects or components. Also, although singular componentsmay be depicted throughout some of the figures, this is for simplicityof illustration and ease of discussion. A person having ordinary skillin the art will readily appreciate that such discussion and depictioncan be and usually is applicable for many components within a structure.

In the following disclosure, a novel biosensor system and method areintroduced. The biosensor system uses a digital filter and selectivewindow to increase signal-to-noise resolution (SNR). The biosensorsystem optionally includes a feedback network and tuning circuit forperforming self-calibration.

FIG. 1 is a diagram showing a biosensor system 10 in accordance withvarious embodiments of the present disclosure. A biosensor 100 of thebiosensor system 10 senses a parameter (e.g., pH) of a solution, andoutputs an according signal (e.g., current, voltage, capacitance, or thelike). In some embodiments, the biosensor 100 is one of an array ofbiosensors. In some embodiments, the biosensor 100 is an ion-sensitivefield effect transistor (ISFET), a nanowire, a nanopore, or the like. Insome embodiments, the biosensor system 10 is integrated into a singleintegrated circuit (IC).

A sensing circuit 110 is electrically connected to the biosensor 100. Insome embodiments, the sensing circuit 110 includes a multiplexer forselecting the biosensor 100 from the array of biosensors. In someembodiments, the sensing circuit 110 includes a converter. In someembodiments, the converter is a current-to-voltage converter, avoltage-to-voltage converter, a capacitance-to-voltage converter, or thelike. In some embodiments, the converter converts an input signal (e.g.,current, voltage, capacitance) to a current. In some embodiments, thesensing circuit 110 further includes an amplifier.

A quantizer 120 is electrically connected to the sensing circuit 110. Insome embodiments, the quantizer 120 includes an analog-to-digitalconverter (ADC). In some embodiments, the ADC is a voltage-mode ADC, acurrent-mode ADC, or the like. The quantizer 120 receives an analogoutput signal of the sensing circuit 110 (e.g., voltage, current), andgenerates a digital output signal D(n) representing the analog outputsignal. In some embodiments, the digital output signal D(n) includes aninteger number of digital bits. In some embodiments, the quantizer 120includes a register for storing and outputting the digital bits.

In many biosensing applications, settling time of an output signal ofthe biosensor 100 (e.g., voltage, current, capacitance), and byextension the digitized version of the output signal (or, “digitalsignal”), is very long relative to output signals of traditionalsensors. Limitations on biosensor performance include chemical flow,bio-reaction, bio-sample, and detection methods. For example, a pHdetector may require about 30 seconds or longer to output a stablevoltage due to at least one of the above factors. The digital signalrepresenting the pH of a solution further includes noise. The noise mayinclude high-frequency noise (thermal or shot noise), and low frequencynoise (long-term drift, ion diffusion, or pixel-to-pixel crosstalk). Thenoise sources are not easily characterized, and noise phenomena aregenerally unique for each pairing of biosensor and chemical solution.

As a result, a post-processing subsystem 130 is electrically connectedto the quantizer 120. A digital filter 131 is electrically connected tothe quantizer 120. In some embodiments, the digital filter 131 includesa low-pass filter, a high-pass filter, a bandpass filter, or the like.In some embodiments, the digital filter 131 includes a finite impulseresponse (FIR) filter. In some embodiments, the digital filter 131includes a moving average filter. In some embodiments, a first digitalsignal Filter_Type is inputted to the digital filter 131 to select atype (e.g., bandpass, low-pass, high-pass) of the digital filter 131. Insome embodiments, a digital signal Filter_order is used to select anorder (e.g., first-order, second-order, etc.) of the digital filter 131.The digital filter 131 outputs a filtered digital signal D_Filter(n).The filtered digital signal D_Filter(n) is a filtered version of thedigital output signal D(n), where type and order of filtering depend onelectrical configuration or design of the digital filter 131.

The filtered digital signal D_Filter(n) is received by a selectivewindow 132 electrically connected to an output terminal of the digitalfilter 131. The selective window 132 is a digital circuit that outputs aselected signal D_Sel(m) from the filtered digital signal D_Filter(n).The selected signal D_Sel(m) includes a sequence of bits of the filtereddigital signal D_Filter(n) that corresponds to a settled region of thefiltered digital signal D_Filter(n). In some embodiments, the sequenceof bits is a time-shifted sequence of bits of the filtered digitalsignal D_Filter(n). For example, the filtered digital signal D_Filter(n)may include digital data corresponding to a period from about when thebiosensor 100 begins sensing pH of a solution (time t1) to about whenthe biosensor 100 stops sensing the pH of the solution (time t2). Theduration of time between the time t1 and the time t2 may be about 1minute, as an example. The selected signal D_Sel(m) may capture a windowof the digital data starting from a time t3 to a time t4. The time t3 isa first period after the time t1, and the time t4 is a second periodbefore the time t2. In some embodiments, the time t4 is simply the timet2. In some embodiments, the first period is greater than about 10seconds. In some embodiments, the first period is greater than about 30seconds.

In some embodiments, the selective window 132 receives at least a starttime signal Start_time. In some embodiments, the selective window 132further receives an end time signal End_time. For example, the starttime signal Start_time may be a digital code representing 30 seconds,and the end time signal End_time may be a digital code representing 40seconds. In some embodiments, the selective window 132 receives aduration signal. For example, the start time signal Start_time may be adigital code representing 30 seconds, and the duration signal may be adigital code representing 10 seconds.

In some embodiments, the start time signal Start_time is a rising edgegenerated a predetermined delay period after beginning sensing by thebiosensor 100. For example, the biosensor 100 may receive an enablesignal at the time t1 to begin sensing the pH of the solution. Theenable signal may be received by a counter. When the counter outputs afirst count signal corresponding to the predetermined delay period(e.g., 30 seconds), a decoder receiving the count signal may output arising edge as the start time signal Start_time. When the counteroutputs a second count signal corresponding to the first period plus asampling period (e.g., 30 seconds plus 10 second), the decoder receivingthe second count signal may output a second rising edge as the end timesignal End_time.

In some embodiments, the selective window 132 samples the filtereddigital signal D_Filter(n) to generate the selected signal D_Sel(m) byan automated process. For example, a variation threshold may be storedin a register. The selective window 132 may compare a first value of thefiltered digital signal D_Filter(n) with a second value of the filtereddigital signal D_Filter(n). When a difference between the second valueand the first value is less than the variation threshold, the selectivewindow 132 may begin capturing the selected signal D_Sel(m). Forexample, when detecting the pH of the solution, when the first value isgreater than the second value by less than about 0.05 (on the pH scale),the selective window 132 may begin capturing the selected signalD_Sel(m).

In some embodiments, the biosensor system 10 is a medical test systemfor determining a medical condition (e.g., positive or negative for avirus, or the like). A decision unit 133 has an input terminalelectrically connected to an output terminal of the selective window132. The decision unit 133 receives the selected signal D_Sel(m), andgenerates a decision signal D_final according to value of the selectedsignal D_Sel(m). For example, if a pH range corresponds to a positivereading for a certain virus, the decision signal D_final may havelogical value one or high when the selected signal D_Sel(m) is withinthe pH range. In some embodiments, the decision unit 133 includes adigital comparator for comparing the selected signal D_Sel(m) with areference value. In some embodiments, the reference value is a digitalcode having a first number of bits equal to a second number of bits ofthe selected signal D_Sel(m). For example, if the selected signalD_Sel(m) is an m-bit signal, the reference value may include m bits.

FIG. 2 is a flowchart of a method 20 in accordance with variousembodiments of the present disclosure. The method 20 is compatible withthe biosensor system 10, and can be used to test a biological substancefor a biological condition. Biological material (e.g., a solution) isinputted 200 to a biosensor, such as the biosensor 100. The biosensorresponds to contact of the biological material with a sensing region ofthe biosensor. For example, the solution may contact a front gate of anISFET, which changes threshold voltage of the ISFET, and alters outputcurrent of the ISFET. A response of the biosensor to the biologicalmaterial is sensed 210. In some embodiments, the response is a voltagesignal, a current signal, a capacitance signal, or the like. Theresponse is converted 220 to a digital signal. In some embodiments, theconversion 220 is performed by an ADC (voltage mode or current mode).

Post-processing 230-260 is performed on the digital signal to generate atest result. The digital signal is filtered 230 to generate a filteredsignal (e.g., the filtered digital signal D_Filter(n)). In someembodiments, the filtering 230 includes low-pass filtering, high-passfiltering, bandpass filtering or the like. Bits of the filtered signalare selected 240 according to a delay setting. In some embodiments, astream of bits is generated by the conversion 220, the stream of bits isfiltered by the filtering 230, and the filtered bits are stored in aregister. Then, an intermediate subset of the stream of bits (e.g., a1024^(th) bit through a 2048^(th) bit) is selected 240. The intermediatesubset corresponds to the delay setting. In some embodiments, thefiltered bits begin to be stored at a clock edge of a selection signal.The clock edge may be delayed from a beginning of sensing 210 by apredetermined delay (e.g., about 30 seconds).

The bits selected by selecting 240 are analyzed 250 to recognize abiological condition. For example, the bits may be compared with a pHvalue. If value of the bits is substantially equal to (or within apredetermined range around) the pH value, the biological condition isrecognized as positive or negative. Presence or absence of thebiological condition (positive or negative screener) is indicated byoutputting 260 a test result. In some embodiments, the outputting 260includes altering a digital display (e.g., a light-emitting diode, apixel array, or the like), emitting an audible noise, or the like. Insome embodiments, the outputting 260 includes outputting a true or falseindicator. In some embodiments, the outputting 260 includes outputting anumber corresponding to, for example, severity of the biologicalcondition.

FIG. 3 is a circuit block diagram showing a biosensor system 30 withinternal calibration in accordance with various embodiments of thepresent disclosure. The biosensor system 30 is similar in many respectsto the biosensor system 10, and like reference numerals refer to likeblocks in FIG. 3 and FIG. 1. In some embodiments, the biosensor system30 includes a feedback block 300 and a tuning circuit 310.

In some embodiments, the feedback block 300 includes a wire, a buffer,other logic gates, or the like. In some embodiments, the feedback block300 includes parallel inputs (e.g., a 4-bit, 8-bit, or greater number ofbits bus). The feedback block 300 provides a path for the tuning circuit310 to receive digital bits generated from the digital signal D(n). Insome embodiments, an input terminal(s) of the feedback block 300 iselectrically connected to an output terminal(s) of the selective window132 for receiving the selected signal D_Sel(m). In some embodiments, theinput terminal(s) of the feedback block 300 is electrically connected toan internal node(s) of the decision unit 133. In some embodiments, theinput terminal(s) of the feedback block 300 is electrically connected tothe output terminal(s) of the filter 131 for receiving the filteredsignal D_Filter(n).

In some embodiments, the tuning circuit 310 adjusts biasing conditionsof the biosensor 100 or the sensing circuit 110 based on the digitalbits received through the feedback block 300. In some embodiments, thetuning circuit 310 has an output terminal electrically connected to areference voltage supply that generates the back gate voltage Vbgbiasing the back gate electrode of the biosensor 100. In someembodiments, the tuning circuit 310 calibrates the biosensor 100 byincreasing or decreasing sensitivity of the biosensor 100 throughaltering the back gate voltage Vbg. In some embodiments, the tuningcircuit 310 has an output terminal electrically connected to a biasgenerator that electrically biases the sensing circuit 110. In someembodiments, the bias generator is a current supply biasing a senseamplifier of the sensing circuit 110. In some embodiments, the tuningcircuit 310 calibrates the sense amplifier of the sensing circuit 110 toincrease or decrease sensitivity of the sense amplifier by modifyingamplitude of the current supply biasing the sense amplifier. In someembodiments, the tuning circuit 310 adjusts biasing of the biosensor 100or the sensing circuit 110 on the basis of calibration (e.g., two-pointcalibration) performed using the digital bits received from the feedbackblock 300. The calibration may be performed, for example, by reading afirst pH of a solution, capturing first digital bits generated duringthe reading of the first pH, reading a second pH of the solution,capturing second digital bits generated during the reading of the secondpH, and performing two-point calibration using the first digital bitsand the second digital bits.

FIGS. 4, 5, and 6 are diagrams showing a calibration path 40, and adevice under test (DUT) 400 of the calibration path 40 in accordancewith various embodiments of the present disclosure. FIG. 4 is a circuitblock diagram of the calibration path 40 in accordance with variousembodiments of the present disclosure. In some embodiments, a DUT 400 isa biosensor, similar to the biosensor 100 of FIG. 1. In someembodiments, the DUT 400 is in contact with a solution having a pH.Front gate, back gate, drain and source electrodes of the DUT 400 arebiased by a front gate voltage source Vfg, a back gate voltage Vbg, adrain voltage Vd, and a source voltage Vs, respectively. In someembodiments, the source voltage is ground. The DUT 400 outputs a currentsignal Id that is proportional to the pH of the solution.

A meter 420 of the calibration path 40 has an input terminalelectrically connected to the DUT 400 for receiving the current signalId. In some embodiments, the meter 420 is an ADC, and receives asampling period signal Ts. The meter 420 outputs a digital currentsignal Id(n) at an output terminal of the meter 420. A filter 431 has aninput terminal electrically connected to the output terminal of themeter 420. In some embodiments, the filter 431 is a moving averagefilter. In some embodiments, the filter 431 has configurable filterorder. For the filter 431 being the moving average filter, the filter431 outputs an averaged current signal Id_avg(n) at an output terminalof the filter 431. A selective window 432 receives the averaged currentsignal Id_avg(n) and a start time signal, and generates a selectedsignal Id_final(m). The selected signal Id_final(m) includes a selectionof digital bits of the averaged current signal Id_avg(n). In someembodiments, a first bit of the selected signal Id_final(m) is storedsubstantially at a rising or falling edge of the start time signal.

FIG. 5 is a circuit diagram showing the DUT 400 of FIG. 4 in accordancewith various embodiments of the present disclosure. In some embodiments,a biosensor 500 is an ISFET. A front gate (fg) of the biosensor 500 isin contact with a solution 510, and is biased by a reference voltageVref generated by a reference voltage supply 501. A back gate (bg) ofthe biosensor 500 is electrically connected to a back gate voltagesupply 502 that generates a back gate voltage Vbg. A source electrode ofthe biosensor 500 is electrically connected to a power supply node(e.g., ground). A drain electrode of the biosensor 500 is electricallyconnected to a current meter 520, and receives a drain voltage Vdgenerated by or copied from a drain bias voltage supply 503.

Threshold voltage of the biosensor 500 varies with pH of the solution510 in contact with the front gate. For a first pH value, the biosensor500 generates a first current in response to the reference voltage Vref.The first current is measured by the current meter 520, which generatesa first signal (e.g., a voltage signal) proportional to the firstcurrent. For a second pH value different from the first pH value, thebiosensor 500 generates a second current different from the firstcurrent in response to the reference voltage Vref.

FIG. 6 is a detailed circuit diagram of the DUT 400 in accordance withvarious embodiments of the present disclosure. In some embodiments, thebiosensor 500 is one of an array of similar biosensors. For example, thebiosensor 500 may be one of an array of ISFETs. To select the biosensor500 for calibration, a select transistor 600 is electrically connectedto the biosensor 500. In some embodiments, a drain electrode of theselect transistor 600 is electrically connected to the drain electrodeof the biosensor 500. A gate electrode of the select transistor 600receives a control signal Sel0.

A current supply 610 that generates a current Ios is electricallyconnected to a source electrode of the select transistor 600. When theselect transistor 600 is turned on, the biosensor 500 draws current fromthe current supply 610. The current drawn by the biosensor 500 isamplified by an amplifier 521 of the current meter 520. In someembodiments, a non-inverting input terminal of the amplifier 521 iselectrically connected to the drain bias voltage supply 503. A virtualshort causes voltage at an inverting input terminal of the amplifier 521to be substantially equal to the drain voltage Vd. A resistor 522 has afirst terminal electrically connected to an output terminal of theamplifier 521, and a second terminal electrically connected to theinverting input terminal of the amplifier 521. Resistance of theresistor 522 may be large (e.g., on the order of hundreds of KΩ).

FIG. 7 is a flowchart of a method 70 for calibrating a biosensor systemin accordance with various embodiments of the present disclosure. Insome embodiments, the method 70 is used with the biosensor system 30 ofFIG. 3 or the calibration path 40 of FIGS. 4-6. Biological material(e.g., a solution) is inputted 700 to a biosensor, such as the biosensor100 or the biosensor 500. The biosensor responds to the biologicalmaterial, and the response is sensed 710. In some embodiments, theresponse is a change in output current of the biosensor. In someembodiments, the sensing 710 is performed by a sensing circuit, such asthe sensing circuit 110 or the current meter 520. In some embodiments,the sensing 710 includes amplifying, such as may be performed by theamplifier 521.

The response (or the amplified response) is converted 720 to a digitalsignal. In some embodiments, the conversion 720 is by an ADC. In someembodiments, the conversion 720 is performed based on a sampling periodsetting, a resolution setting, or the like, which is applied to thecircuit (e.g., the ADC) performing the conversion 720.

The digital signal is filtered 730 to generate a filtered signal (e.g.,the filtered signal D_filter(n) or the averaged current signalId_avg(n)). In some embodiments, the filtering 730 includes low passfiltering, high pass filtering, bandpass filtering, moving averagefiltering, or the like.

Bits of the filtered signal are selected 740 according to a startsetting. In some embodiments, the start setting is a pulse or signaledge that is delayed from when the biosensor begins sensing by apredetermined settling period (e.g., on the order of tens of seconds).In some embodiments, the start setting is a digital signal indicatingbit positions (e.g., a start bit and an end bit) of the filtered signal.

Calibration bits are fed back 750 to a tuning circuit (e.g., the tuningcircuit 310). In some embodiments, the feeding back 750 is by a feedbacknetwork, such as the feedback block 300. In some embodiments, thecalibration bits are digital bits of the digital signal, filtered bitsof the filtered signal, or selected bits of a selected signal generatedby selecting 750.

Biasing conditions of the biosensor or sensing circuit are adjusted 760based on calibration information stored in the calibration bits. In someembodiments, the adjusting 760 includes changing back gate voltage Vbgof an ISFET, or current supply applied to an amplifier (e.g., theamplifier 521) of the sensing circuit.

Embodiments may achieve advantages. Post-processing performed by thepost-processing subsystem 130 smooths the digital signal read from thebiosensor 100 or 500, and selects bits of the filtered signal thatcorrespond to a more settled region of the digital signal. As a result,accuracy of the biosensor systems 10, 30 is better compared to otherapproaches. The feedback block 300 and tuning circuit 310 allow for fastcalibration of an array of biosensors. Performing post-processing in thedigital domain increases flexibility and tunability. Signal-to-noiseratio (SNR) is also improved by speed of the quantizer 120.

In accordance with various embodiments of the present disclosure, amethod includes inputting biological material to a biosensor, sensing aresponse of the biosensor to the biological material by a sensingcircuit, converting the response to a digital signal, filtering thedigital signal by a digital filter to generate a filtered signal, andselecting bits of the filtered signal according to a start time togenerate a selected signal. In an embodiment, the method includesdetermining a biological condition according to analysis of the selectedsignal, and outputting an indication of the biological condition. In anembodiment, the method includes feeding back the selected signal to atuning circuit. In an embodiment, the method includes tuning a biasingcondition of the biosensor according to the selected signal. In anembodiment, the method includes tuning a biasing condition of thesensing circuit according to the selected signal. In an embodiment, themethod includes feeding back the filtered signal to a tuning circuit. Inan embodiment, the method includes tuning a biasing condition of atleast the biosensor or the sensing circuit according to the filteredsignal. In an embodiment, filtering the digital signal includesselecting at least one of an order of the digital filter or a type ofthe digital filter.

In accordance with various embodiments of the present disclosure, amethod includes transmitting a first analog signal indicating abiological parameter to a sensor circuit, converting the first analogsignal to a second analog signal by the sensor circuit, wherein thesecond analog signal is a different type of signal than the first analogsignal, transmitting the second analog signal to a quantizer circuit,converting the second analog signal to a first digital signal by thequantizer circuit, transmitting the first digital signal to a digitalfilter circuit, filtering the first digital signal by the digital filtercircuit, transmitting the filtered first digital signal to a selectivewindow circuit, selecting a signal portion of the filtered first digitalsignal by the selective window circuit, wherein the selecting of thesignal portion is based on a time offset, transmitting the signalportion to a decision circuit, and outputting a decision signal based onthe signal portion by the decision circuit. In an embodiment, the firstanalog signal is a current and the second analog signal is a voltage. Inan embodiment, the method includes receiving a start time signal by theselective window circuit, wherein the time offset is based on the starttime signal. In an embodiment, the start time signal includes a risingedge signal. In an embodiment, the start time signal indicates aduration of time. In an embodiment, converting the first analog signalto a second analog signal is based on a feedback signal received by thesensor circuit from a tuning circuit. In an embodiment, the feedbacksignal is based on the filtered first digital signal. In an embodiment,the feedback signal is based on the signal portion.

In accordance with various embodiments of the present disclosure, amethod includes sensing a biological material with a biosensor togenerate a first output signal, the first output signal representing afirst duration of time, wherein the biosensor operates at a firstbiosensor condition, converting the first output signal to a secondoutput signal, wherein the conversion is based on a first conversionparameter, quantizing the second output signal into a digital signal,filtering the digital signal with a digital filter, selecting a portionof the filtered digital signal representing a second duration of timethat is smaller than the first duration of time, and based on theselected portion of the filtered digital signal, adjusting the firstbiosensor condition to a second biosensor condition that is differentthan the first biosensor condition. In an embodiment, the methodincludes, based on the selected portion of the filtered digital signal,outputting a signal representing a biological condition. In anembodiment, the method includes, based on the selected portion of thefiltered digital signal, adjusting the first conversion parameter to asecond conversion parameter that is different than the first conversionparameter. In an embodiment, the digital filter includes a movingaverage filter

As used in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB or both A and B. Furthermore, to the extent that “includes”, “having”,“has”, “with”, or variants thereof are used in either the detaileddescription or the claims, such terms are intended to be inclusive in amanner similar to the term “comprising”. Moreover, the term “between” asused in this application is generally inclusive (e.g., “between A and B”includes inner edges of A and B).

Although the present embodiments and their advantages have beendescribed in detail, it should be understood that various changes,substitutions, and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims. Moreover, the scope of the present application is not intendedto be limited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods, and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A method comprising: inputting biologicalmaterial to a biosensor; sensing a response of the biosensor to thebiological material by a sensing circuit; converting the response to adigital signal; filtering the digital signal by a digital filter togenerate a filtered signal; and selecting bits of the filtered signalaccording to a start time to generate a selected signal.
 2. The methodof claim 1, further comprising: determining a biological conditionaccording to analysis of the selected signal; and outputting anindication of the biological condition.
 3. The method of claim 1,further comprising: feeding back the selected signal to a tuningcircuit.
 4. The method of claim 3, further comprising: tuning a biasingcondition of the bio sensor according to the selected signal.
 5. Themethod of claim 3, further comprising: tuning a biasing condition of thesensing circuit according to the selected signal.
 6. The method of claim1, further comprising: feeding back the filtered signal to a tuningcircuit.
 7. The method of claim 6, further comprising: tuning a biasingcondition of at least the biosensor or the sensing circuit according tothe filtered signal.
 8. The method of claim 1, wherein filtering thedigital signal comprises selecting at least one of an order of thedigital filter or a type of the digital filter.
 9. A method comprising:transmitting a first analog signal indicating a biological parameter toa sensor circuit; converting the first analog signal to a second analogsignal by the sensor circuit, wherein the second analog signal is adifferent type of signal than the first analog signal; transmitting thesecond analog signal to a quantizer circuit; converting the secondanalog signal to a first digital signal by the quantizer circuit;transmitting the first digital signal to a digital filter circuit;filtering the first digital signal by the digital filter circuit;transmitting the filtered first digital signal to a selective windowcircuit; selecting a signal portion of the filtered first digital signalby the selective window circuit, wherein the selecting of the signalportion is based on a time offset; transmitting the signal portion to adecision circuit; and outputting a decision signal based on the signalportion by the decision circuit.
 10. The method of claim 9, wherein thefirst analog signal is a current and the second analog signal is avoltage.
 11. The method of claim 9, further comprising: receiving astart time signal by the selective window circuit, wherein the timeoffset is based on the start time signal.
 12. The method of claim 11,wherein the start time signal comprises a rising edge signal.
 13. Themethod of claim 11, wherein the start time signal indicates a durationof time.
 14. The method of claim 9, wherein the converting the firstanalog signal to a second analog signal is based on a feedback signalreceived by the sensor circuit from a tuning circuit.
 15. The method ofclaim 14, wherein the feedback signal is based on the filtered firstdigital signal.
 16. The method of claim 14, wherein the feedback signalis based on the signal portion.
 17. A method comprising: sensing abiological material with a biosensor to generate a first output signal,the first output signal representing a first duration of time, whereinthe biosensor operates at a first bio sensor condition; converting thefirst output signal to a second output signal, wherein the conversion isbased on a first conversion parameter; quantizing the second outputsignal into a digital signal; filtering the digital signal with adigital filter; selecting a portion of the filtered digital signalrepresenting a second duration of time that is smaller than the firstduration of time; and based on the selected portion of the filtereddigital signal, adjusting the first biosensor condition to a secondbiosensor condition that is different than the first biosensorcondition.
 18. The method of claim 17, further comprising: based on theselected portion of the filtered digital signal, outputting a signalrepresenting a biological condition.
 19. The method of claim 17, furthercomprising: based on the selected portion of the filtered digitalsignal, adjusting the first conversion parameter to a second conversionparameter that is different than the first conversion parameter.
 20. Themethod of claim 17, wherein the digital filter comprises a movingaverage filter.